Flexible lithium‐ion batteries: Materials design, interfacial regulation, and strain‐adaptive device architectures

Abstract Flexible lithium‐ion batteries (FLIBs) are emerging as promising power sources for wearable, foldable, and deformable electronics, where stable electrochemical output must be maintained under repeated bending, twisting, folding, and stretching. However, conventional lithium‐ion batteries built on rigid current collectors, brittle electrodes, and flammable liquid electrolytes suffer from interfacial delamination, electrode cracking, electrolyte leakage, and rapid performance decay under dynamic deformation, necessitating the rational redesign of FLIBs across electrodes, electrolytes, and cell architectures. In this review, recent advances in FLIBs are summarized from these perspectives. Design strategies for flexible anodes and cathodes are first discussed, including multidimensional conductive scaffolds, high‐capacity active materials, self‐supporting frameworks, and nanoarray architectures. Gel and solid‐state electrolytes are then reviewed with emphasis on the balance among ionic conductivity, mechanical compliance, interfacial stability, and safety, followed by thin‐film, fiber‐shaped, and stretchable cell architectures that adapt to distinct deformation modes through structural engineering. Beyond these component‐level strategies, the mechano‐electrochemical coupling governing deformation‐induced failure is analyzed, spanning failure mechanisms at the device, electrode, and electrolyte/interface levels, finite‐element modeling, and in situ/operando characterization. Finally, remaining challenges in high‐loading electrodes, interfacial stability, standardized mechano‐electrochemical evaluation, scalable fabrication, and device integration are outlined. By correlating materials design, interfacial regulation, mechano‐electrochemical understanding, and cell‐level architecture, this review provides design principles for high‐performance FLIBs toward practical wearable and deformable energy‐storage systems.